The present invention relates to a device and method of calculating the amount of toner consumption with high accuracy so that the actual amount of consumption can be ascertained. The present invention also relates to an image forming apparatus using such a device and a method.
An image forming apparatus which forms an image through use of toner must manage the life of a toner cartridge by ascertaining the amount of toner consumption or the amount of remaining toner in order to facilitate maintenance, such as toner replenishment, or preservation of image quality. Japanese Patent Publication No. 2002-174929A discloses a method for calculating toner consumption with simple configuration which enable accurate determination of toner consumption.
A relationship between the number of a printed dot and the amount of toner consumption is nonlinear, and the relationship also changes depending on the state of another printed dot adjacent to that printed dot. In light of this relationship, the method classifies a train of printed dots into three patterns; that is, an isolated dot, two consecutive dots, and an dot of intermediate value. The number of dots formed is counted on a per-pattern basis. The amount of toner consumption is determined on the basis of the counted values.
In such an image forming apparatus, the toner filled in the toner cartridge is gradually consumed and decreased as a result of repeated formation of an image. When the amount of toner filled in the cartridge has decreased to a certain level or less, a message “Please replace the toner cartridge” appears on a display of the image forming apparatus, thereby alerting the user.
Even in view of effective utilization of resources, the user desires to accurately recognize the amount of toner consumption and replace a toner cartridge at an appropriate time. This publication teaches a pattern into which a train of printed dots is arranged is classified into three categories. There is disclosed determination of the amount of toner consumed per page during a certain job period on the basis of the pattern in which a train of printed dots is arranged. Specifically, the amount of toner actually consumed by an image formation area of a recording medium is detected, and the amount of toner consumption is subtracted from a toner initial value filled in the toner cartridge, thereby determining the amount of remaining toner. However, the image forming apparatus is susceptible to occurrence of a “fogging” phenomenon; that is, adhesion of toner to a non-image formation area (white background) of a recording medium other than the image formation area.
Therefore, in order to manage the life of a toner cartridge by ascertaining the amount of toner remaining in the image forming apparatus, the amount of toner consumed by fogging as well as the amount of toner consumed by the image formation area must be taken into consideration. However, this publication fails to describe means for determining the amount of toner consumed by fogging. Therefore, this technique suffers a problem of inability to appropriately calculate the toner consumption with high accuracy.
However, if variations have arisen in the amount of toner transferred to an image carrier in an image forming apparatus which superposes toner images of multiple colors on the image carrier, the electric potentials of exposed portions vary in the next color process, thereby requiring a stricter control operation. Moreover, there may be a case where the density of an image varies for reasons of fatigue in a photosensitive member, a time-varying change in toner, and variations in the temperature and humidity of a neighborhood of the apparatus. Therefore, there has hitherto been proposed a technique for stabilizing the density of an image by controlling a density control factor which affects the density of a toner image; e.g., a charging bias, a development bias, and the amount of exposure, as required.
Such a technique is for controlling an operation for supplying toner to the inside of a development device or consumption of toner in the development device, by forming a patch toner image on an image carrier and optically measuring the density of the patch image through use of a sensor. For instance, Japanese Patent Publication No. 2001-42579A describes an image forming apparatus comprising: a charger for charging the surface of a photosensitive member; an exposer for forming an electrostatic latent image on the surface of the photosensitive member; a developer for forming a toner image by rendering the electrostatic latent image visible with toner; a density detector for detecting the density of an image by taking, as a patch image, the toner image formed on the photosensitive member by the developer or the toner image formed as a result of transfer of the toner image of a transfer medium; and a controller for controlling the density of the toner image to a target level on the basis of a result of detection performed by the density detector, wherein the patch image is formed from a plurality of single dot lines spaced apart from each other.
As mentioned above, in the image forming apparatus, a patch image to be used for controlling density is prepared as a preparing operation prior to formation of an image in the image formation area. Toner is also consumed even at the time of formation of the patch image. However, according to the prior art, even when the amount of toner consumption is sought, no consideration has been paid to the amount of toner consumed to form the patch image. Therefore, there is a problem of a failure to appropriately calculate the amount of toner consumption with high accuracy. There is another problem of a failure to accurately manage the life of the toner cartridge.
In the image forming apparatus of this type, if an offset exists in positions, where images of different colors are to be transferred, during transfer of an image on a recording medium, a color displacement arises, to thereby deteriorate image quality. In order to correct such a color displacement, Japanese Patent Publication No. 7-32656A discloses formation of a registration mark to a paper transport belt (i.e. a member for moving a recording member).
The image forming apparatus is further provided with a cleaning blade for removing the toner still remaining on the image carrier (i.e., the photosensitive member). If pressure at which a cleaning blade comes into contact with the image carrier is too large, the cleaning blade will vibrate, thereby failing to perform cleaning operation properly. For these reasons, there is a problem of deterioration of image quality, which is caused when toner remains on the image carrier. To solve the problem, Japanese Patent Publication No. 2001-42729A describes prevention of vibration of the cleaning blade by accumulating, at all times, toner at a position immediately below an area where the image carrier comes into contact with the cleaning blade, thereby causing the toner to act as a lubricant. Although not described in this publication, there is a conceivable method for previously imparting toner to be used for preventing vibration of the cleaning blade, with a view toward rendering image quality stable by rendering contact between the photosensitive member and the cleaning blade smooth in the initial state of the image forming apparatus achieved at shipment from a factory.
As mentioned above, the image forming apparatus uses toner in an application other than the application for formation of an image in an image formation area. Specifically, toner is imparted to a predetermined area, such as the neighborhood of an area where the paper transport belt or the image carrier comes into contact with the cleaning blade, with a view toward achievement of stable image quality. However, this technique does not take into consideration the amount of toner consumed at a predetermined position for achieving image quality, which has already been described, at the time of determination of the amount of toner consumption. Therefore, there has been a problem of a failure to appropriately and accurately calculate the amount of toner consumption. There is also a problem of a failure to accurately manage the life of the toner cartridge.
Japanese Patent Publication No. 2001-42579A describes formation of a solid image patch (a Vdc patch) as a technique for rendering the density of an image stable by controlling a density control factor which affects the density of the toner image; e.g., a charging bias, a development bias, and the amount of exposure, as required. Moreover, forming a fine-line patch (E patch) as a patch image to be used for controlling density in conjunction with a solid image is also known. The fine-line patch is formed by a so-called “one-on ten-off” method, wherein, e.g., a patch image corresponding to one line is formed, and no image is formed in an area corresponding to ten lines in a secondary scanning direction.
The image forming apparatus described in this publication is equipped with a main controller having an image memory for storing image data to be transmitted from an external calculator, and an engine controller for controlling an image formation section (engine) in accordance with a signal output from the main controller. Moreover, the previously-described image patch is described as being prepared by a patch generation module of the engine controller. That is, the density pattern of an image is determined by the engine controller.
In the image forming apparatus of this type, the density and line width of the toner image vary in accordance with the temperature and humidity of an image environment or the number of times the image carrier and a developing agent have been used. For this reason, a patch image called a gradation patch is formed, thereby measuring the density of the patch image and determining a density control pattern. Japanese Patent Publication No. 8-254861A describes writing of a gradation pitch into a RAM of a control circuit (main controller). That is, the density control pattern is determined by the main controller.
As mentioned previously, before forming an image in the image formation area, the image forming apparatus forms a patch image to be used for controlling a density as a preparing operation. The patch image is separated into an image of gradation patch prepared by the main controller, and a solid image and a fine-line patch image, which are prepared by the engine controller, and the images are stored in the respective storages. However, neither the main controller nor the engine controller is given information about a patch image prepared by the counterpart controller. For this reason, the total amount of toner consumed by an overall patch image is not recognized.
As mentioned above, toner is consumed even when a patch image is formed. However, according to these techniques, at the time of determination of the amount of toner consumption, no consideration has been paid to the amount of toner consumed by the main controller to form the gradation patch image and the amount of toner consumed by the engine controller to form the fine-line patch image. Therefore, there has been a problem of a failure to accurately and appropriately calculate the amount of toner consumption. Moreover, there is a problem of a failure to accurately manage the life of the toner cartridge.